Ok.
Regarding correction the existing footage, a guy in the Blackmagic forum suggest trying optical flow for framerate correction. I'll try that.
Regarding future projects:
So in general I'll shoot at 2.7k@30fps in the future. Along the lines that most users will use primarely HD and some 4k that seems a good compromise.
If I need a slomo shot I'll need to adjust upfront to 60fps.
Question though, sometimes one realises later that slomo would be nicer. What than? Sometimes one can not retake shots? Would it not be best to shot as high a framerate as possible? Downgrade should always be possible, but upgrade would be hard to do and result in poor quality.
Thanks again!